The modal analysis is based on a load case to which the modal analysis analysis type is assigned. Multiple modal analysis load cases can be used for the model.
In the Load Cases tab of the 'Load Cases and Combinations' dialog box, you can assign the analysis types and define additional parameters. To do this, select the load case on the left in the ' list '.
Categories
In this section, basic settings are to be made for the dynamic analysis of the load case.
Analysis type
If the add-on 'Modal analysis' is activated in the model basic data, the modal analysis is available for selection in the list. Assign this analysis type to each load case for which a dynamic analysis is to be carried out.
Modal Analysis Settings
In the list of 'Modal Analysis Settings' ( MOS ), select the specifications according to which the load case is to be examined. These are, for example, the eigenvalue method, mass matrix setting or mass conversion. These parameters are described in chapter Modal Analysis Settings.
Use the
button to add new modal analysis settings, and the
button to edit the selected setting.
Import masses only from load case/load combination
In the list of defined load cases and combinations, specify which load is to be considered as a mass in the modal analysis. In the picture # extbookmark manual|image027386|Adopting masses from load case # shows how you apply the load of the "Self-weight" load case for a dynamic load case.
Dead load
This section is only visible if you want to consider the masses directly from the same modal analysis load case (see image # extbookmark manual|image027385|Load case of the type 'modal analysis' for direct load transfer#). The effect is analogous to the function, as described in the section Deadweight of the RFEM manual is described for a load case of the structural analysis.
Options
If you activate the 'Consider imperfection' check box, you can select an imperfection case from the list that is to be used together with the load case in the modal analysis. The functions of an imperfection case are taken into account in chapter Imperfection as well as in chapter [[ #/de/downloads-und-infos/documents/online-handbooks/rfem-6/000243 Imperfection cases {%\} of the RFEM manual. You can use the
button to create a new imperfection case.
The 'Structural Modification' check box enables you to take into account a stiffness adjustment or special handling of nonlinearities in the load case. These functions are described in the Structure Modifications chapter. Select the structural modification from the list or create a new modification type using the
button.
Special Options
If you activate the check box 'Consider initial state from', you can select a load case from the list whose stiffnesses represent the starting position for the modal analysis of the selected load case.
The
button next to the list opens the 'Initial State Settings' dialog. Define the 'Type of Initial State' that is available. Only the 'Stiffness' type is currently available.
In chapter Consider initial state you will find further explanations as well as an example of how failing elements affect the modal analysis.